2010-08-10 22:43:22Basic Rebuttal No.5: How reliable are climate models? REVISION 2
gpwayne
Graham Wayne
graham@gpwayne...
81.132.177.33

Climate Models: Learning From History Rather Than Repeating It

Argument No. 5: How reliable are climate models?

Climate models are mathematical representations of the interactions between the atmosphere, oceans, land surface, ice – and the sun. This is clearly a very complex task, so models are built to estimate trends rather than events. For example, a climate model can tell you it will be cold in winter, but it can’t tell you what the temperature will be on a specific day – that’s weather forecasting. Climate trends are weather, averaged out over time - usually 30 years. Trends are important because they eliminate - or "smooth out" - single events that may be extreme, but quite rare. 

Climate models have to be tested to find out if they work. We can’t wait for 30 years to see if a model is any good or not; models are tested against the past, against what we know happened. If a model can correctly predict trends from a starting point somewhere in the past, we could expect it to predict with reasonable certainty what might happen in the future.

So all models are first tested in a process called Hindcasting. The models used to predict future global warming can accurately map past climate changes. If they get the past right, there is no reason to think their predictions would be wrong. Testing models against the existing instrumental record suggested CO2 must cause global warming, because the models could not simulate what had already happened unless the extra CO2 was added to the model. Nothing else could account for the rise in temperatures over the last century.

Where models have been running for sufficient time, they have also been proved to make accurate predictions. For example, the eruption of Mt. Pinatubo allowed modellers to test the accuracy of models by feeding in the data about the eruption. The models successfully predicted the climatic response after the eruption. Models also correctly predicted other effects subsequently confirmed by observation, including greater warming in the Arctic and over land, greater warming at night, and stratospheric cooling.

The climate models, far from being melodramatic, may be conservative in the predictions they produce. For example, here’s a graph of sea level rise:


Sea level change. Tide gauge data are indicated in red and satellite data in blue. The grey band shows the projections of the IPCC Third Assessment report (Copenhagen Diagnosis 2009).

Here, the models have understated the problem. In reality the events are all within the upper range of the model’s predictions. There are other examples of models being too conservative, rather than alarmist as some portray them. All models have limits - uncertainties - for they are modelling chaotic systems. However, all models improve over time, and with increasing sources of real-world information such as satellites, the output of climate models can be constantly refined to increase their power and usefulness.

Climate models have already predicted many of the phenomena for which we now have empirical evidence. Climate models form a reliable guide to potential climate change.

2010-08-10 23:20:48Use of Graphs
John Russell

jr@johnrussell...
82.70.63.102

Graham> Take a look at the suggestion I've made about the use of graphs on the 'length' thread. 

Here I would break the graph down into three stages starting in 1990. I would say...

[Graph 1 - show just the IPCC greyed out section] In 1990, based on models, the IPCC projected sea level rise of between 1 and 6 cm over the next 20 years. 

[Graph 2 - superimpose satellite data] Since then measurements from satellites have shown a steady rise in sea level of 6 cm.

[Graph 3 - superimpose tide readings] The satellite measurements are confirmed by actual tide readings over the same 20-year period.

Hope this helps.

I worry about, "...the models have understated the problem". So models got it wrong, eh? I'd just remove that statement and say, "Here the models are all on the worst case edge of..."

Best wishes,

JR

2010-08-11 00:33:03complexity
gpwayne
Graham Wayne
graham@gpwayne...
81.132.177.33

Hi John - I saw your remarks about graphs, but in this case your suggestion would make the explanation look more technical than I believe it needs to be - at this level. Would your data breakdown not be more suited to the intermediate level?

As for "...the models have understated the problem", the text is consistent with John's original intermediate post. I've noticed that sometimes we can avoid putting things a certain way because we know how our detractors will manipulate our equivocation. Personally, I don't think it's a good idea to let them dominate the agenda like that, putting us on the back foot and avoiding saying the 'reasonable' thing. 'Understated' is what they did - if people want to pick holes in that wording as you suggest, they are not going to buy into the explanation anyway, because they'll be deniers.

2010-08-11 03:46:48careful
Robert Way

robert_way19@hotmail...
24.224.230.112
Be careful with this modeling topic as a new paper is coming out http://climateaudit.org/2010/08/09/mckitrick-et-al-2010-accepted-by-atmos-sci-lett/  which shows that models are overpredicting warming...
2010-08-11 08:52:34Observed temperature vs. models, tuning on hindcasting
doug_bostrom

dbostrom@clearwire...
184.77.83.151

Nice writeup Robert.

It's hard to say that observed atmospheric temperatures are tracking worst case scenario, they're really not. However, when we look at sea level it's arguable the "missing heat" is in the ocean. I'm not sure if nuance of this kind will fit into a basic discussion but I am sure the rebuttal will suffer kickback if atmospheric temperature is lumped in w/worst case.

Also, you might want to be absolutely sure that folks don't misunderstand hindcasting, might be worth a quick mention of the Pinatubo event being faithfully reproduced in hindcasts.

2010-08-11 16:04:29Re-writing the originals
gpwayne
Graham Wayne
graham@gpwayne...
81.132.177.33

Doug - you and Robert both raise an interesting issue, perhaps inadvertently. My 'take' on this subject was written to be consistent with John C's original numbered item. I have not tried to update or modify his explanation, in part because I'm not qualified to do so, and in part because I think it's important that the basic and intermediate versions are consistent. If McKitrick's paper is correct, then the Item 5 needs revision because it says the opposite, and I could adjust the basic version accordingly if required.

I think putting the Pinaturbo event in is a good idea - I'll sort that out.

2010-08-12 23:58:33Being consistent with my Intermediate rebuttal
John Cook

john@skepticalscience...
121.222.17.49
Graham, don't feel beholden to my existing rebuttal - feel free to "go rogue" (Sarah Palin style) and take a different approach. I'm happy to update/edit the Intermediate rebuttal to keep things consistent - I'm sure many or most of my rebuttals could do with a bit of work.
2010-08-13 03:46:16Being consistent with my Intermediate rebuttal
John Russell

jr@johnrussell...
84.92.176.215

Can I add that in the basic rebuttals I've done so far, I've always used the intermediate rebuttal (and the juicy bits in the comments that follow it) as my source material. Certainly, personally, I could not 'go rogue' even if I wanted -- I don't have the academic knowledge to go back to basic principles: I have to understand what's been written on the site and then -- using the writing skills I have gained in my career -- ruthlessly distil it into my own words, without being hidebound by any scientific conventions. 

The great thing about having no emotional attachment to the subject matter is that one can be ruthless without feeling loss.   

2010-08-13 16:45:45About humility
gpwayne
Graham Wayne
graham@gpwayne...
81.132.177.33

Damn, I feel exactly the same as John R. I'm a layman, and every time I've trespassed into more detailed technical areas, or commented on the science itself, I ended up making a fool of myself. I count on two things: that the existing rebuttals are accurate (and tested over time, which is reassuring) and that quite a few people around here know more about all this than I ever will - as demonstrated by excellent and kind corrections that I'm thankful for.

My skills - such as they are - involve stringing a few words together in a way that isn't too obscure. I will not be re-writing any climate science any time soon (not in this life, actually).

2010-08-14 21:06:32Revised version explained
gpwayne
Graham Wayne
graham@gpwayne...
81.152.239.255

In the revision I've tried to accomodate most of the comments, as follows:

Added Mt. Pinaturbo calibration.

Re-worked section on low-balled estimates - used term 'conservative' to make point and avoid implication models failed

Removed worst case edge...

(I have not added more graphs, as I feel one is probably enough in the basic version, just as a passing example rather than presenting an argument per se).

2010-08-15 04:17:12Another home run
doug_bostrom

dbostrom@clearwire...
184.77.83.151
Ready to go, looks to me.
2010-08-17 15:39:22Bump
doug_bostrom

dbostrom@clearwire...
184.77.83.151
Aging in the can...
2010-08-17 15:50:30Typo - Mt Pinatubo
BaerbelW

baerbel-for-350@email...
93.231.132.221

This reads very well, I just spotted a typo:

the eruption of Mt. Pinaturbo

2010-08-17 16:17:51Typo fixed
gpwayne
Graham Wayne
graham@gpwayne...
86.156.59.156
Cheers Baerbel - now fixed. The missing graph is now uploaded too.
2010-08-18 10:33:20
Brendon

bpywell@iinet.net...
124.170.75.247

One minor spelling correction, sucessfully should be successfully.

I would also leave out the "Where we have had the time, " since I don't think it's adding anything to the main argument.

Oh, and for my own clarification, the Pinatubo prediction, was this really a climate prediction - as in did they do this before the changes to the climate occurred?

2010-08-18 15:16:30On time
gpwayne
Graham Wayne
graham@gpwayne...
86.156.59.156

Hi Brendon - thanks for the typo - well spotted. On the other point, I think perhaps it was badly worded and looked colloquial. What I meant - and I've changed the text accordingly - is 'where sufficient time has elapsed' i.e. to test the models against real world events.

And one such event is Pinatubo, where they did indeed feed the eruption factors into the climate models, which then successfully predicted the reduction in temperature. There's a good site that describes the process - oh wait, we're on it! http://www.skepticalscience.com/argument.php?a=13

2010-08-20 19:36:51
Ari Jokimäki

arijmaki@yahoo...
192.100.112.211

"The climate models, far from being melodramatic, are generally conservative in the predictions they produce."

Are you sure about this? My initial feeling is that it depends a lot on the subject. For example, tropical troposphere hot spot shows generally better in models than in observations (however, they have been getting closer to each other in recent years and the situation currently is tolerable - regardless of what the new McKitrick paper says).

It also bothers me a bit that both this article and the intermediate version don't actually have much discussion about the uncertainties in climate modelling even if the question addressed is "how reliable are climate models".

2010-08-20 20:31:20Typo - plural for "phenomenon"
BaerbelW

baerbel-for-350@email...
109.41.43.59

Hi Graham,

shouldn't the plural "phenomena" be used in the last sentence?

Climate models have already predicted many of the phenomenon for which we now have empirical evidence. Climate models form a reliable guide to potential climate change.

2010-08-20 21:57:48A few suggestions.
John Russell

jr@johnrussell...
84.92.176.215

1) "...it can’t tell you with any certainty what the temperature will be on a specific day "; sounds like it can't be certain but will make a prediction. I suggest: " "...it can’t tell you what the temperature will be on any specific day ".

2) I suggest the first para is quite wordy. How about ending it...

Climate trends are weather, averaged out over time. Trends are important because they eliminate - or "smooth out" - single events that may be extreme but quite rare. A trend of 30 years is the avearge length considered valid in climate science.

3) "We can’t wait for 30 years (a period considered long enough to establish a trend) to see if a model is any good...". You've just explained what you've put above, so I suggest condensing it: "We can’t wait for the 30 year trend to establish if a model is accurate..." . and to continue; "...or not; so to start with models are tested against the past, against what we know happened. (note the semi colon -- because there are perhaps too many commas in the original).

4) The start of your third para appears overly repetitive of the second -- I suggest you take a look.

Others have commented on most of the other points. Overall I think it works and is just right for the basic level.

Best wishes,

JR

2010-08-21 18:08:01New revisions
gpwayne
Graham Wayne
graham@gpwayne...
217.44.86.17

My thanks to Ari, Baerbel and JR. All points now addressed.

(JR - speaking writer to writer, nothing better than cutting out the duff stuff to watch the text come into focus. Good calls).

2010-08-21 22:17:08Gets my vote
John Russell

jr@johnrussell...
84.92.176.215

Green thumb, sir?

2010-08-22 01:03:28Why yes, JR....
gpwayne
Graham Wayne
graham@gpwayne...
217.44.86.17
...don't mind if I do, JR...
2010-08-22 03:35:20
Ari Jokimäki

arijmaki@yahoo...
91.154.108.109
Thumbs up (#001).
2010-08-22 03:59:54Comment
Robert Way

robert_way19@hotmail...
142.162.177.145
thumbs up
2010-08-25 23:04:15Pattern of warming
James Wight

jameswight@southernphone.com...
58.105.164.221
I can think of one other thing you might want to mention, but it’s probably not necessary in a basic rebuttal. Climate models have also successfully predicted many aspects of the pattern of warming: greater warming in the Arctic, greater warming over land, greater warming at night, as well as stratospheric cooling etc.
2010-08-25 23:22:21James - agreed
gpwayne
Graham Wayne
graham@gpwayne...
217.44.86.17
Good call James - I put just a mention in, but definitely worth doing.
2010-08-26 10:39:30Published
John Cook

john@skepticalscience...
124.187.125.135
Great stuff Graham and the team :-)